Vibration procedures are commonly used for the production of tubes from concrete mix to condense the concrete. For that, a vertically standing filling form is used which has walls for shaping the outer and inner contour of the tube. Fresh concrete mix, which is continuously set into vibrations, is poured in the area between these walls. One or more vibrators, most of the time located in the inner space of the filling form, are used to generate the vibrations. Because of the large mass of the tubes to be manufactured, such a vibration system has to be capable to set the total mass of concrete mix and filling form into vibration, which goes along with a high usage of energy. Additionally, a considerable part of the energy is lost, because it is not converted into vibrations in the optimal frequency coverage but in acoustic vibrations causing flexural mode, heat and noise. Such vibration procedures are therefore a noise burden and an expenditure of energy, which connects the production of concrete tubes by this procedure with high cost and health risks.
A further disadvantage of such procedures is, that the quality of the condensation can vary if the vibration device is operating under the constant feed of concrete mix: Since the mixture that was poured in first and is located on the lower end of the form is exposed to the vibrations for a longer period of time than the mixture that is poured in later, the condensation is higher on the lower end, which leads to different material characteristics within the tube.
An improvement regarding the use of energy and uniformity of the material characteristics can be achieved, for example, with the arrangement described in WO 92/18307, which also uses a vibration procedure and consists of inner and outer form-shaping elements that are movable towards each other, but in fact only the inner form-shaping elements can be moved, while the outer element corresponds with a sheathing. The vibrations are generated in a vibration head of an inner form-shaping element and are restricted to a small area along the tube, which in the cause of the concrete feed is shifted along the axis of the tube. To generate the static pressure necessary for the condensation, the upper part of the vibration head has a helical and conical form and the mixture flowing in from above is transported down by rotation and the static pressure is also generated because of the conicity. The condensation itself is then achieved by the vibration.
But the arrangement described in WO 92/18307, which reflects the next phase of technology, has disadvantages as well: Vibrations, whose generation is associated with a high use of energy and noise, is used here for the condensation as well. Additionally, the stress on the material of the form-shaping device is relatively high, since coupled rotation-vibration movements occur in a part of the inner form-shaping element. In other parts rotation only. Due to the construction, the production of the upper end of a tube, which commonly has an acute end contour, is difficult as well. Since the helical vibration head partially stands out from the form towards the end of the fabrication it is questionable, if the static pressure necessary for the condensation corresponds with the one used in the inside of the form, since not enough concrete mixture can be filled in from above. Additionally, it is complicated to remove the inner form-shaping element opposite to the form-shaping device, and during that process possibly clear away material from the inner contour of the tube. It is therefore not suitable for the production of continuous tubes either.
Generally, all vibration procedures and arrangements using such procedures have further disadvantages. Besides noise, which endangers the health of persons that are near the devices that carry out vibration procedures and makes sound insulation measures necessary, the high stress on parts of such devices is an essential disadvantage as well. Additionally, continuous vibration damages are caused by the vibrations, which could lead to crack formation in the sheathing.
Another possibility is the appearance of acceleration differences with areas in which the condensation occurs insufficient due to the construction of the vibration arrangement. This effect is reduced with a vibration device whose linear expansion is shorter than the tube to be produced and that moves relative to the sheathing, but is not completely oppressed. Especially in the areas of the joints is the condensation generally more difficult than in the remaining tube section, zones can even be formed in the joints in which the mixture is considerably less condensed. A further disadvantage is the fact that the natural vibration of the system depends on the filling level of the filling form and that it changes with it. To achieve a proportionate condensation the tuning characteristic of the system is dynamically adapted to the filling level, which requires a very big effort.
Additionally, limits are set for vibration procedures by the procedure itself: Requirement for the usage of this procedure is that the concrete mixture can be condensed sufficiently by vibration. But this requirement is not fulfilled with some mixtures—for example, with mixtures for the production of high-performance or fiber concrete. Furthermore entails the production of thin walled tubes difficulties: In order to not impede the flow of the granular and rather viscous concrete mix that is to be filled in the area between the sheathing, and the vibration core, whose diameter corresponds with the diameter of the produced tube, this area must have a minimum diameter.
A roller head procedure is also used for the production of tubes from concrete mix. In this procedure a rotating pressing tool condenses the concrete mix by pressing it against sheathing. But here as well entails the condensation difficulties in the area of the joints. Furthermore is the bandwidth of processible mixture qualities limited.